1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, a developing unit and a process cartridge.
The "electrophotographic image forming apparatus" is an apparatus for forming an image on a recording medium by using an electrophotographic image forming system. For example, the electrophotographic image forming apparatus may be an electrophotographic copying machine, an electrophotographic printer (for example, a laser beam printer or an LED printer), an electrophotographic facsimile or an electrophotographic word processor.
The "process cartridge" incorporates therein an electrophotographic photosensitive member and a developing means for developing a latent image formed on the electrophotographic photosensitive member as a cartridge unit which can be detachably mounted to a main body of an electrophotographic image forming apparatus. It incorporates therein, in addition to the developing means and the electrophotographic photosensitive member, at least one of a charge member for charging the electrophotographic photosensitive member and a cleaning member for removing developing agent remaining on the electrophotographic photosensitive member, as a cartridge unit which can detachably be mounted to a main body of an electrophotographic image forming apparatus.
2. Related Background Art
A conventional electrophotographic image forming apparatus such as an electrophotographic copying machine, a laser beam printer or the like includes a photosensitive drum. Well-known processes such as charging, exposure and development are successively effected regarding the photosensitive drum, thereby forming a toner image on the photosensitive drum and transferring the toner image onto a recording medium. Thereafter, residual toner remaining on the photosensitive drum is removed by a cleaning device. In this way, the image is formed.
In such electrophotographic image forming apparatuses, recently, a process cartridge has been adopted to make the apparatus compact and simplify the maintenance. In the process cartridge, the photosensitive drum and the process means (such as a charge member, a developing member and a cleaning member) acting on the photosensitive drum are integrally incorporated as a cartridge unit which can detachably be mounted to a main body of the image forming apparatus by an operator himself.
In such electrophotographic image forming apparatuses, powder developing agent is used. The developing agent is contained in a developing container of the process cartridge or a developing unit and is sent, by a developing agent convey means, to a developing agent bearing member which holds the developing agent. The developing agent held on the developing agent bearing member is shifted to an electrostatic latent image forming portion, where the electrostatic latent image formed on an image bearing member is visualized. Thereafter, the visualized image is transferred onto a transfer material, such as a paper sheet, by a transfer means and then is fixed to the transfer material by a fixing device. In this way, a series of image forming processes are finished, and a desired image can be obtained.
In such electrophotographic image forming apparatuses, as the number of prints or copies are increased, the developing agent in the process cartridge or the developing unit is decreased, thereby causing the poor printing. To avoid this, generally, there is provided a developing agent remaining amount detecting portion for informing the operator of the fact that the remaining amount of developing agent becomes small before poor printing is generated. For example, in a method for detecting the remained amount of the developing agent, the change in amount of developing agent in the developing container is measured as a change in electrostatic capacity to detect the remaining amount of the developing agent.